The pyrido[2,1-a]isoquinoline derivatives of formula II
whereinR2, R3 and R4 are each independently selected from the group consisting of hydrogen, halogen, hydroxy, lower alkyl, lower alkoxy and lower alkenyl, wherein lower alkyl, lower alkoxy and lower alkenyl may optionally be substituted by a group consisting of lower alkoxycarbonyl, aryl and heterocyclyl, and the pharmaceutically acceptable salts thereof are disclosed in PCT International Patent Appl. WO 2005/000848.